Recent and continuing increases in computer processing power and speed, in the speed and capacity of primary memory, and in the size and complexity of computer software has resulted in the need for faster operating, larger capacity secondary memory storage devices; magnetic disks forming the most common external or secondary memory storage means utilized in present day computer systems. Unfortunately, the rate of improvement in the performance of large magnetic disks has not kept pace with processor and main memory performance improvements. However, significant secondary memory storage performance and cost improvements may be obtained by the replacement of single large expensive disk drives with a multiplicity of small, inexpensive disk drives interconnected in a parallel array, which to the host appears as a single large fast disk.
Several disk array design alternatives were presented in an article titled "A Case for Redundant Arrays of Inexpensive Disks (RAID)" by David A. Patterson, Garth Gibson and Randy H. Katz; University of California Report No. UCB/CSD 87/391, December 1987. The article, incorporated herein by reference, discusses disk arrays and the improvements in performance, reliability, power consumption and scalability that disk arrays provide in comparison to single large magnetic disks.
An additional disk array arrangement, referred to as parity striping, is presented in an article titled "Parity Striping of Disc Arrays: Low-Cost Reliable Storage with Acceptable Throughput" by Jim Gray, Bob Horst and Mark Walker; Tandem Computers, Inc., Tandem Technical Report No. 90.2, January 1990. In the parity striping system, only parity information is striped across the disks, but the parity is mapped as large contiguous extents. Data is not striped across the disks at all.
The individual magnetic disks utilized in the various disk array configurations discussed in the articles referred to above often provide individual interrupt signals, each interrupt signal indicating that a specific disk has completed an operation or encountered a problem. A method for combining these individual disk interrupt signals into a single system interrupt signal for notifying the host system processor that the array has completed its operation or encountered a problem is desired.